Field of the Invention
The present invention relates to a test apparatus.
Description of the Related Art
With a high-speed digital signal transmission system that transmits a high-speed digital signal across a given long distance, marked transmission loss occurs in a transmission path. This leads to degradation in the high-frequency characteristics, resulting in degradation in waveform quality. FIG. 1 is a diagram for describing the effects of the loss that occurs in the transmission path. Description will be made regarding an arrangement in which the signal to be transmitted is configured as a binary digital signal that is switchable between high level and low level. Such a system requires a long signal transition time at a reception end (RX) as compared with signal transition at a transmission end (TX) when the digital signal transits from high level to low level or otherwise from low level to high level. This leads to waveform dulling at the reception end (RX). The signal received at the reception end (RX) is compared with a predetermined threshold value VTH at a timing of a sampling clock CKS so as to judge whether the signal level is high level or low level.
An increase in the transmission distance leads to marked waveform dulling. In this case, the transmission of the received signal does not complete at the reception end RX within the sampling timing, leading to false detection of high level or low level. With a transmission path that involves large transmission loss, in some cases, the transmission time becomes longer than each sampling interval TS.
Known examples of an approach proposed in order to solve the aforementioned problem include a pre-emphasis technique. Specifically, a pre-emphasis circuit is provided to the transmission end so as to boost the high-frequency component of a transmission signal according to the attenuation characteristics of the transmission path (high-frequency emphasis). Furthermore, an equalizer is provided to the reception end so as to compensate for degradation in the high-frequency characteristics of the transmission path.
However, such a method requires the transmission end and the reception end to have a high driving capability and a high operation speed that are sufficient for the signal characteristics required for the transmission signal. On the other hand, the driving capability and the operation speed are limited by the semiconductor process. Thus, in a case in which such a transmission system requires a large amount of compensation, in some cases, such a method cannot be employed.
Patent documents listed below discloses the related arts.
Patent Document 1
Japanese Patent Application Laid Open No. 2001-156596l 
Patent Document 2
Japanese Patent Application Laid Open No. 2011-215127
Patent Document 3
Japanese Patent Application Laid Open No. 2010-103663
Patent Document 4
Japanese Patent Application Laid Open No. S60-254279